| In the multi-storey and tall building structures of reinforced concrete, the foundation of double or more columns usually needs to be designed into a whole because of being subjected to the influence of many factors such as the distance of column axes, the load of superstructure and the property of subsoils. This kind of double or more columns combined foundation is widely used in the engineering. However, at present there is not a unified rule about the design-calculation method for the combined foundation(including the combined shallow foundation and the combined pile foundation ), and also there is not a relevant provision in the "Code for Design of Building Foundation"(GB 50007-2002), the calculation method that designers adopt are not the same with each other, and this leads to great difference in the design of combined foundation. Therefore, it seems very essential to carry on a deep systematic study on this kind of combined foundation design-calculation method. In the thesis, the design-calculation method for the double-column combined foundation is studied, a design-calculation method for the double-column combined shallow foundation and the double-column combined pile cap is discussed, and the application of the spatial truss model theory in the design of double-column combined pile cap is preliminarily discussed. This thesis has summarized the relevant part of current code and also in the international and domestic study or application of design theory about double-column combined foundation.A systematic analysis has been made of two kinds of calculation methods for the double-column combined shallow foundation—one is based on the national code and the other based on the ACI code, suggesting a hidden beam set up between the two columns and meanwhile a design-calculation method for hidden beam being discussed and a comparatively intact design-calculation method of double-column combined shallow foundation has been put forward on the basis of such comparison and analysis. Moreover, the author of the thesis has studied the calculation model of two design schemes for setting up or not setting up a hidden beam for the double-column pile cap, and also has discussed the relevant calculation method, and in combination with an engineering example for comparative analysis, thus drawing the conclusion that it is more reasonable to adopt the design scheme for setting up a continuous hidden beam under the two columns of double-column combined pile caps. In this thesis, the finite element software ANSYS has been used to analyze the force-transmission mechanism of double-column six pile caps through 3D nonlinear finite element, and has established the spatial truss calculation model of double–column six pile caps. In combination with an engineering example, the design steps and calculation method have been presented for the spatial truss model of double-column combined pile cap . Designers may refer to the design-calculation methods which are suggested in this thesis in terms of double-column combined shallow foundation and double-column combined pile caps.
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